Microsoft released updates for both Office 2004 and Office 2008 for the Mac late on Tuesday.
The updates are available at the Mactopia downloads site. Version 11.5.1 is for Office 2004 and version 12.1.2 is for Office 2008.
The update for Office 2008 is 153 MB and can be found in the column labelled "Newest" at the link above. The update for Office 2004 is 15 MB.
Microsoft said that the updates include fixes for vulnerabilities that could allow an attacker to overwrite the contents of memory with malicious code.